Liquid crystal displays (LCDs) are typically used as the information display in various devices such as computers and vehicle and airplane instrumentation. One type of LCD called the twisted nematic liquid crystal display (TN-LCD) often has the drawback of a narrow range of viewing angles. Thus an improved design called the in-plane switching liquid crystal display (IPS LCD) has been developed in order to provide a broad range of viewing angles. The IPS LCD typically has a plurality of common electrodes and a plurality of pixel electrodes all disposed on one of two opposite substrates, for driving liquid crystal molecules contained in a liquid crystal layer between the two substrates. The resulting electric field is substantially planar and parallel to surfaces of both substrates. The IPS LCD typically has a broad range of viewing angles.
According to the particular electrode array of its pixel electrodes and common electrodes, an IPS LCD can be classified as a single-domain type or a two-domain type. FIG. 6 is a schematic, exploded isometric view of a typical IPS LCD 10. The IPS LCD 10 includes a first substrate 11, a second substrate 12 opposite to the first substrate 11, and a liquid crystal layer 13 sandwiched between the substrates 11, 12. The liquid crystal layer 13 includes a multiplicity of liquid crystal molecules 18. A first and a second polarizers 14, 15 are formed at outer sides of the substrates 11, 12 respectively. A plurality of pixel electrodes 16 and common electrodes 17 are disposed parallel to each other at an inner surface of the second substrate 12. A first alignment layer (not shown) is disposed at an inner surface of the first substrate 11. A second alignment layer (not shown) is disposed at the inner surface of the second substrate 12, the second alignment layer covering the pixel and the common electrodes 16, 17. Original rubbing directions of the first alignment layer and the second alignment layer are parallel to each other. Long axes of the liquid crystal molecules 18 adjacent to the alignment layers are approximately parallel to the first and the second substrates 11, 12. Polarizing axes of the first and second polarizers 14, 15 are perpendicular to each other.
When no voltage is applied to the pixel and common electrodes 16, 17, the long axes of the liquid crystal molecules 18 maintain an angle relative to the pixel and common electrodes 16, 17. Light beams are emitted from a back light module (not shown) below the second substrate 12. When the light beams pass through the liquid crystal layer 15, their polarizing directions do not change, and the light beams are absorbed by the first polarizer 14. Thus the IPS LCD 10 is in an “off” state, and cannot display images.
As shown in FIG. 7, when a voltage is applied to the pixel and common electrodes 16, 17, an electric field E1 is generated between the pixel and common electrodes 16, 17. A direction of the electric field E1 is parallel to the second substrate 12, and perpendicular to the pixel and common electrodes 16, 17. The long axes of the liquid crystal molecules 18 twist to align in the direction of the electric field E1. When light beams pass through the liquid crystal layer 13, the polarization state of the light beams is converted to match the polarizing axis of the first polarizer 14. Thus the light beams pass through the first polarizer 14 to display images, and the IPS LCD 10 is in an “on” state.
When the voltage is applied, all the liquid crystal molecules 18 are aligned in the same new direction according to the electric field E1. When the voltage is switched off and the IPS LCD 10 returns to the “off” state, the liquid crystal molecules 18 twist to align in the original direction according to the first and second alignment layers. The amount of time needed for all the liquid crystal molecules 18 to realign is relatively long. This means that the response time of the IPS LCD 10 is unduly long.
What is needed, therefore, is an IPS LCD which overcomes the above-described problems.